Drive units of this kind, which enable two objects to rotate relative to one another and, at the same time as and/or independently of the rotation, to move linearly relative to one another, can be used in a wide variety of applications.
A typical field of use is in screw-type closing means which are used in systems for automatically closing beverage containers. For this purpose, the working element, typically a rotationally symmetrical shaft, is coupled to a closing head in a rotationally fixed and axially non-displaceable manner in relation to the rotation axis of the working element. The closing head is matched to the shape of the respective beverage containers, such as PET or glass bottles. Since the working element, and therefore the closing head, moves rotationally and linearly with respect to the first housing element, the beverage container, which is arranged in a non-moveable manner with respect to the first housing element, can be closed. In this case, it is necessary to ensure that the closure cover is screwed on as far as its end position, so that the liquid within the beverage container is sufficiently effectively sealed off from environmental influences, such as ambient air and germs, until the promised expiration date. In addition, the so-called sealing ring has to be handled without being damaged and snap on in an interlocking manner. In addition, the screw-on torque must not be unduly high for the user of the bottle. The effective capacity of such screw closing means can be up to 65,000 bottles per hour.
A further field of application for drive units of this generic type is in screwing together two or more machine parts which are provided with in each case an internal and external thread or a passage hole. Turning screws in threaded holes should be mentioned by way of example here, with it often also being necessary to monitor the process in respect of the screw-in torque in this application, for example in the case of safety-relevant components in the vehicle or the aircraft industry.
Further fields of application for drive units of this generic type can be found in automation engineering, for example in automatic assembly and test machines, or in productronics, for example in automatic component mounting machines or in in-circuit testers.
A drive unit of this generic type is known from DE 100 25 351 A1 where this apparatus has a linear motor and a rotational motor. Both the linear motor and the rotational motor from DE 100 25 351 A1 are formed by permanent magnets, which are arranged on the working element, in this case a rotationally symmetrical shaft, and coils which surround the permanent magnets and are arranged in a housing. In order to ensure a constant drive power of the motors over the possible travel of the working element, the cylindrical air gap area which forms between the permanent magnets and the coils always has to be constant. In DE 100 25 351 A1, this is achieved by the axial extent of the permanent magnets extending beyond the axial extent of the coils in accordance with the value of the maximum travel. However, this results in high costs, design and assembly is complicated and a large axial installation space is required.